I don't know about "tour buses" but there are SITA buses between Amalfi and Pompei: amalficoastweb.com/orari_sita_bus_timetables… (bottom right-hand timetable). You'll notice they are timed for people working in Naples, i.e. there is nothing between the 06:40 departure from Sorrento (arr. 08:30) and the 15:00! And there is only one return from Pompei, at 16:50.
I imagine that that they drop you near the Pompei (sic) station on the other side of the archaeological site from the Circumvesuviana (which has a stop, Pompeii Scavi, close to the main entrance). From Pompei FS (station) it's about a 10 minute walk to the Piazza Amfiteatro entrance to the site.
Edited: 6:18 pm, August 18, 2013